In the case that a paver is processing hot paving material working components of the paver need to be heated until the paving material does not tend any more to glue. The temperature of the paving material is about 170° C. Heating normally starts prior to the beginning of a paving process. Heating continues during the paving process. The mentioned working components may be the smoothing plate of the paving screed, the tampering bars, the pressing bars or the container for the paving material. It is conventional in practice to mount at least one electric flat heating rod on the heating area of the smoothing plate. The flat heating rod is supplied with rotary current by a rotary current generator of the paver. At least one electric flat heating rod also is inserted into the tampering bar or into the pressing bar if a pressing bar is provided. The known flat heating rod consists e.g. of a drawn round tube which is pressed into a flat configuration such that flat upper and lower sides are formed. A heating coil made of a coil spring-like wound heating wire is inserted in serpentine line configuration into the flat tube and is secured and positioned by an insulating filling of ceramic powder. Such flat heating rods only can be manufactured with a width somewhat below 20 mm. Due to the design of the flat heating rod effective heat transfer takes place essentially only in the central region of the narrow contact area while in the edge regions of the contact area hardly a heating effect can be generated. An unfavourable heating picture results in the heating area of the working component. Furthermore, relatively long heating-up periods have to be encountered and irregular heating pictures. A further drawback is that the heating rods are formed with an integrated slim connection housing at one rod end which connection housing protrudes vertically from the heating rod and which easily can be damaged by aggressive medias as used in a paver. In case of a replacement of a flat heating rod the connection housing also has to be replaced together with the electric connection cable. Due to the relatively bad heat transfer of the flat heating rod a relatively high electric supply power is needed. Since conventionally, a plurality of such heating rods is implemented into a paver, the plurality of heating rods results in an undesirably high load of the rotary current generator.
The flat heating rod conventionally is secured by means of tensioning screws protruding from the smoothing plate via an intermediate metal profile onto the smoothing plate. The tensioning screws have to be provided at the side of the heating rod. A direct heating in the alley defined along the array of the tensioning screws in the heating area is impossible.
In a paver known from U.S. Pat. No. B1-6,318,928 several heating elements are mounted on the smoothing plate of the paving screed via a heat distributing plate. Each heating element is a rigid, hollow metal rod containing an interiorly placed resistive coil. The heating elements are heating rods which are conventional in this technique. The heating elements allow to heat a limited heating area only and with a relatively badly defined heating picture.
DE 46 03 33 C discloses an electric heating body containing an elastic insert made from asbestos. An insulated resistive wire is wound around the insert. The insulated heating coil is surrounded by a coat made of thin sheet metal. The coat is confined in a strong metallic sleeve. During manufacturing of the heating element the metallic sleeve temporarily is deformed under pressure such that after relief of the pressure the asbestos insert presses the heating coil against the sheet metal coat.